There are several known methods of thermal spraying. In these methods, a coating material, such as a metal in the form of powder is fed into a flame. The flame melts the metal powder, so that it can be deposited onto a surface as a coating. An important measurement of quality in most thermal spraying methods is the adhesion of the coating on the surface. A higher velocity thermal spray is generally preferred as the impingement of the coating material onto the deposition surface at higher velocity, typically results in coatings which exhibit better adhesion to the deposition surface. An additional concern common to most methods of thermal spraying is to avoid overheating the coating material which can lead to vaporization or oxidation and reduce the overall quality of the coating produced. In addition, it is also desirable to produce small droplets of material to ensure even coating and maximize surface to volume ratios in order to enhance adhesion and quality of the coating produced.
In the field of thermal spraying, there are several methods that attempt to optimize the velocity of the deposition without degrading the quality of the material to be deposited. Most thermal spray methods seek to reduce the residence time in the heating device to minimize the formation of oxides in the coating material. Also, many thermal sprays use a coating material in powder form in order to optimize the surface to volume ratio of the coating material. However, the use of powder may require special delivery and metering equipment and can lead to delivery problems within the thermal spray device.
Systems known to exist which may be somewhat functionally similar to the technique of this application utilize pulsed detonation technology (rather than resonant deflagration) to achieve high velocity, molten material. Pulsed detonation systems, while achieving higher temperatures and velocities than the instant invention are far more complex to achieve and control. They require multi-valved actuation and forced fuel and air. As such they are non-mobile and very expensive. Their operational frequencies (pulse rates) are also considerably lower than pulsejet based combustion systems of the instant invention so that high deposition rates are more difficult to achieve.
U.S. Pat. No. 2,926,855 discloses an Atomizing and Spraying Apparatus wherein an acoustic jet resonator has a chamber and tube which are both excited at their natural frequency and heated by the pulsating flow of exhaust gases from the internal combustion device to spray a liquid. This reference teaches spraying a liquid material using exhaust fumes.
U.S. Pat. No. 6,745,951 B2 to Barykin et al discloses using a detonation spray gun to produce high energy explosions to thermally spray a coating initially supplied as a powder. This reference requires the use of coating material in a powder form and special precautions to detonate gases without causing continuous explosions or a distribution of the powder within the barrel of the device due to the highly explosive nature of the reactant gases.
U.S. Pat. No. 4,232,056 teaches a method for using a thermospray gun to melt a metallic coating material and impinge the molten coating particles against a metallic substrate. The thermospray gun utilizes an oxy-fuel gas flame spraying gun or electric arc gun in a continuous process.
U.S. Pat. No. 6,579,573 B2 teaches a method for forming a nanostructured coating using ultrasound to form a solution with dispersed nanostructured particles using an ultrasonic horn as a sound source. This reference discloses a high velocity oxy-fuel (HVOF) for depositing a coating. High velocity oxy-fuel processes are continuous and require high outputs of energy to maintain a high velocity stream.
None of the references employ a pulsejet having metal wire fed into the combustion chamber to produce high volume, high velocity surface deposition of a protective metallic coating.